1. Field of the Invention
This invention relates to a method of making acoustical tile normally utilized in ceiling constructions. More particularly, this invention relates to a method and apparatus for creating a textured surface on the wet tile during its manufacture. It relates still more particularly to the texturing of acoustical tile in a wet state as an aqueous plastic acoustical composition of mineral fiber material.
2. Description of the Prior Art
A popular type of acoustical tile is made following generally the procedure set forth in U.S. Pat. Nos. 1,769,519; 1,996,033; and 3,246,063. Generally, according to the of these patents, a mixture of mineral wool (preferably granulated), fillers, certain coloring materials if desired, and a binder, preferably of an amylaceous nature such as thick boiling starch, is used to form the body of the tile. Various other materials may be added to give certain properties to the tile. Generally, in manufacture the composition is placed upon suitable trays, which have previously been covered with a backing sheet such as paper; textured or surface smoothed to provide a pleasing surface such as that resembling travertine stone; placed in an oven; and then dried or cured at a temperature of about 250.degree.-300.degree. F. for from about 12 to about 18 hours. The dried sheets, called slabs, are removed from the tray or other mold; dressed on both faces and sides to provide smooth surfaces and obtain desired thickness and edge treatments; finish painted and the like, and cut into tiles of a desired size.
It is often desirable to impart a pleasing texture to such product for aesthetic reasons, and, to some extent, for improved acoustical properties. Methods known for imparting a texture include a patterned sand blasting of the dried and cured tile, rough screeding of the wet aqueous plastic composition, and pressing of the wet slab under a solid press roll having the reverse of the desired pattern in the roll. The sand blasting procedure must be very carefully controlled, and it is wasteful of the eroded material. The solid press rolls do not achieve high fidelity in the reproduction of the pattern and are very limited in the number of patterns available without extensive capitalization and inventory of rolls. The screeding procedure is limited as to the number of distinctive patterns that can be formed.
The screeding procedure, in more detail, involves screeding of the wet aqueous plastic composition mass with an oscillating bar. This produces a fine, lightly striated appearance depending upon the speed of the trays on the assembly line passing beneath it, the pressure of the bar and the nodule size of the granulated wool. It is at times desirable to produce a tile having a rougher, more stone-like appearance. This may be done by screeding with the edge of the screed. Instead of passing smoothly over the mass, the edge of the screed drags up some of the wool, resulting in rather large fissures or valleys in the surface and extending into the tile interior. This is more readily accomplished using larger or looser nodules of the granulated wool. It will be appreciated that the screeding process provides a more random, nonrepeating texturing of the surface than the other methods. However, it is quite limited in the number of patterns and variation in depth bas-relief.
Thus it is an object and advantage of the present invention to provide means for imparting a textured surface on cast acoustical composition which has the natural appearance and randomness of the screeding procedure yet providing infinitely variable number of three-dimensional texture patterns.
It is another object of this invention to provide an apparatus for producing acoustical composition having a textured surface which is not wasteful of the eroded material and which does achieve a high fidelity in the reproduction of natural appearing patterns having portions thereof being raised and portions thereof being in relief.
It is a further object and advantage of the present invention to provide a method and an apparatus for texturing ceiling tile in a moving wet pulp ceiling tile board manufacturing line in which surface patterns are produced that may vary from a very light, shallow, striated texture on the one hand to on the other hand, a very coarse, bold and deep texture resembling the naturally-looking fissures with undercuts of natural stone or rock.
Various other objects and advantages will readily occur to those skilled in the art to which this invention pertains from the following descriptions.
In carrying out this invention in one basic form, at least one hollow roll cylinder having a plurality of holes randomly placed over the surface therein is positioned above a moving wet pulp ceiling tile board line; and the roll cylinder is equipped with an air pressure line, whereby pressurized air moving through the holes in the roll impinges upon the surface of the wet pulp and produces a texture on the pulp surface. By varying the line speed of the ceiling tile board line, or the speed of the spinning roll, or both, different texture patterns varying from a linear striated series of furrows to a coarse, pitted, naturally-appearing fissure of natural rock is produced. Differing degrees of texture from a light, shallow, frost to very coarse, bold and deep textures may be produced by varying the air pressure within the roll, or the distance from the roll to the pulp, or both.